Method of electroplating non-conductive plastic molded products

ABSTRACT

A method of electroplating non-conductive plastic moldings, the method comprising the steps of: applying a catalyst useful for electroless plating to non-conductive plastic moldings using a colloidal solution containing a precious metal compound and a stannous compound; forming an electrically conductive coating on the surface of the moldings using an electroless copper plating solution containing a copper compound, a saccharide having a reducing property, a complexing agent and an alkali metal hydroxide; and electroplating the coated moldings. According to the method, an electroplated coating excellent in appearance and properties can be formed on non-conductive plastic moldings by a simple procedure.

This is a national stage application of Ser. No. PCT/JP97/01187 filedApr. 7, 1997.

FIELD OF THE INVENTION

The present invention relates to a method of electroplatingnon-conductive plastic moldings and an electroless copper platingsolution suitable for use in said electroplating method.

BACKGROUND ART

Among methods of electroplating non-conductive plastic moldings to forma decorative coating, a widely employed method comprises, in succession,degreasing, etching, optionally neutralizing and pre-dipping, thenapplying a catalyst for electroless plating using a colloidal solutioncontaining a tin compound and a palladium compound, and optionallyactivating (accelerator treatment), followed by electroless plating andelectroplating.

In such plating method, electroless copper plating solutions arefrequently used which contain a reducing agent having a high reducingpower such as paraformaldehyde. When this electroless copper platingsolution is used, copper is deposited in the initial plating stage on ahighly catalytic palladium portion of tin/palladium colloid coatingapplied as the catalyst. However, copper is continuously deposited byreduction due to the reducing action of the reducing agent with highreducing power and thus a copper layer is formed not only on thepalladium portion but also in the transverse direction. As a result,copper is also deposited on an inherently non-catalytic tin portion sothat a so-called bridge deposit is formed which is likely to provide aspongy coating. When electroplating is conducted on the electrolesslyplated coating having the bridge deposit, pit-like fine agglomerates(called stardust) are partially deposited in a great number, therebytending to render the coating irregular. The plated coating thus formedon the plastic substrate often shows an inferior appearance comparedwith a plated coating on a metallic substrate.

To prevent the creation of such inferior appearance, attempts have beenmade to brush the surface of the substrate electrolessly plated withcopper before electroplating. However, the attempt is disadvantageous ininvolving a cumbersome step.

Further, the electroless copper plating solution contains, as a reducingagent, paraformaldehyde which is highly toxic and presumablycarcinogenic. A further problem is that considerable labor is entailedin removing the metal ions in the disposal of waste water because acompleting agent having a high complexing power such as EDTA has beenused to solubilize the copper ions.

When electroless nickel plating is conducted in place of electrolesscopper plating, stardust scarcely develops because of a lesser degree ofbridge deposits so that the resulting electroplated coating isesthetically superior in appearance to the electroplated coating formedon the electrolessly plated copper coating. However, electroless nickelplating disadvantageously requires more catalyst than electroless copperplating, thereby incurring higher costs. Further, when copperelectroplating is conducted after electroless nickel plating, the nickelcoating is eroded by the galvanic potential difference due to lowerpotential of the nickel coating than the copper coating, thereby tendingto induce coat peeling and resulting in blisters.

A method is known which comprises immersing a substrate in a colloidalsolution containing a precious metal to deposit a colloid coating ofprecious metal, and directly electroplating the coated substrate withoutconducting electroless plating (Japanese Unexamined Patent PublicationNo.267393/1991). However, this method is defective as follows. Since thecoating has a low electrical conductivity and electroplating proceeds ata low deposition rate, the feeding points of electrical power require alarge area when plastic moldings of great area are electroplated.Furthermore, a substantial time is taken to electroplate the entiresubstrate surface of such plastic moldings and it is difficult to form auniform coating over the entire substrate surface. Moreover, theprocedure is performed under narrowly limited conditions, and thecontrol of treating solutions and the working conditions are verycumbersome.

DISCLOSURE OF THE INVENTION

A primary object of the present invention is to provide a method ofelectroplating non-conductive plastic moldings by a simple procedure,the method being capable of forming a coating excellent in appearanceand properties.

The present inventors conducted extensive research in view of theforegoing prior art problems and found the following. A suitableelectrically conductive coating can be formed without developing abridge deposit by a method comprising applying a catalyst useful forelectroless plating to non-conductive plastic moldings, andelectrolessly plating the moldings using an electroless copper platingsolution of novel makeup containing a saccharide having a reducingproperty as a reducing agent. Further, when the surface of saidelectroless-plated coating is directly electroplated, a decorativecoating of excellent appearance can be easily formed. Since theelectroless copper plating solution to be used in this method contains asaccharide with relatively low reducing power as a reducing agent, ahigh stability of the plating solution is assured and the solution canbe easily controlled. In addition, because a hydantoin compound having arelatively low complexing power can be used as a complexing agent forcopper, the electroless copper plating solution has excellent propertiesincluding high deposition capability and ease of effluent treatment.Based on these novel findings, the present invention was accomplished.

According to the present invention, there are provided:

(1) a method of electroplating non-conductive plastic moldings, themethod comprising the steps of: applying a catalyst useful forelectroless plating to non-conductive plastic moldings using a colloidalsolution containing a precious metal compound and a stannous compound;forming an electrically conductive coating on the surface of themoldings using an electroless copper plating solution containing acopper compound, a saccharide having a reducing property, a complexingagent and an alkali metal hydroxide; and electroplating the coatedmoldings: and

(2) an electroless copper plating solution which is an aqueous solutioncomprising 0.1 to 5 g/l, calculated as copper metal, of a coppercompound, 2 to 50 g/l of a complexing agent, 3 to 50 g/l of a saccharidehaving a reducing property and 10 to 80 g/l of an alkali metalhydroxide.

There is no limitation on the type of non-conductive plastic moldings tobe treated by the method of the invention. A highly decorative platedcoating can be easily formed even on large-size moldings having a greatarea. For example, the method of the invention can be applied to plasticautomotive components recently widely used in the automobile industry.Examples of such large-size plastic materials include front grilles,emblems and other automotive parts, exterior components of electronicdevices, knobs and like parts to be electroplated for decoration,materials to be plated for giving corrosion resistance or for adding anew function, etc.

The kind of plastic materials to be treated is not limited, and variousplastic materials heretofore known can be treated. Examples of plasticsare general-purpose plastics heretofore extensively used for chemicalplating such as ABS resins, general-purpose engineering plastics havinga heat resistance at a temperature of 150° C. or less, such aspolyamides (nylon PA), polyacetals (POM), polycarbonates (PC), modifiedpolyphenylene ethers (PPE), polybutylene terephthalates (PBT) and thelike, super engineering plastics having a heat resistance at atemperature of 200° C. or more, such as polyphenylene sulfides (PPS),polyether sulfones (PES), polyether imides (PEI), polyether etherketones (PEEK), polyimides (PI), liquid crystal polymers (LCP) and thelike, polymer alloys such as polycarbonate/ABS and the like. It issuitable to use, among these plastics, plastics of a grade proper forplating such as ABS resins and the like which can avoid the decrease inthe adhesion of the plated coating and the degradation of coatingappearance by means of etching or other pretreatment of the plastics.

In the plating method of the invention, first, a pretreatment isconducted in the conventional manner. Namely the surface of a substrateto be treated is cleaned to remove extraneous matter such asfingerprints, fats and oils and like organic substances, dust depositeddue to electrostatic action and so on. Conventional degreasing agentscan be used as a treating solution. Degreasing is conducted in theconventional manner using a conventional degreasing agent, for example,an alkaline degreasing agent or the like.

Subsequently the surface of the substrate to be treated is etched whenso required. The etching treatment selectively dissolves the surface ofresin substrate to achieve an anchor effect. This treatment can improvethe adhesion of the plated coating, the appearance of the coatingsurface and the like. The etching procedure is carried out byconventional methods. For example, the substrate to be treated isimmersed in a properly heated mixed solution of chromic acid andsulfuric acid. When a substrate of ABS resin is treated, the etchingtreatment dissolves out polybutadiene as the constituent due tooxidative effect of chromic acid, giving anchor pores of about 1 toabout 2 μm in pore size to the resin substrate, while the polybutadieneis caused to undergo oxidative decomposition, producing a polar groupsuch as a carbonyl group. Consequently a colloidal solution containing aprecious metal compound and a stannous compound is easily adsorbed inthe subsequent step.

When substrates of general-purpose engineering plastics or superengineering plastics are treated, they are often difficult to etch and,therefore, are preferably pre-etched in the conventional manner prior toetching, when so required. The pre-etching treatment swells a skin layeror a crystal-oriented layer on the surface of the resin substrate usingan organic solvent. The pre-etching can be conducted usually using asolvent of high polarity such as dimethyl sulfoxide. The pre-etchingtreatment can enhance the etching effect.

Also, resin substrates containing inorganic materials, glass fibers andthe like can be treated by a proper etching method selected fromconventional methods.

After etching, the resin substrate is washed to remove the etchingsolution such as chromic acid or the like remaining on the surface ofresin substrate. The chromic acid can be easily removed from the surfacewhen cleaning is effected using a diluted solution of hydrochloric acidor a solution containing a reducing agent such as sodium bisulfite.

Subsequently a catalyst useful for electroless plating is applied to thesubstrate to be treated using a colloidal solution containing a preciousmetal compound and a stannous compound. Conventional catalyst solutionsuseful for electroless plating can be used as the colloidal solution.Such conventional catalyst solutions usually contain a precious metalcompound such as a platinum compound, gold compound, palladium compound,silver compound and the like which are known to have a catalyticproperty for electroless plating. Specific examples of the platinumcompound to be incorporated in the catalyst solution includechloroplatinate. Specific examples of the gold compound are chloroaurateand salt of gold sulfite. Specific examples of the palladium compoundare palladium chloride and palladium sulfate. Specific examples of thesilver compound are silver nitrate and silver sulfate. The preciousmetal compounds can be used either alone or in combination. It ispreferred in the invention to use a catalyst solution containing apalladium compound as the precious metal compound. The amount of theprecious metal compound used is not limited. A suitable amount is about100 to about 500 mg/l calculated as metal.

Preferred examples of the stannous compound to be incorporated in saidcolloidal solution are stannous chloride and stannous sulfate. Thesecompounds can be used alone or in combination. Among them, stannouschloride is preferred. The amount of the stannous compound used may beusually about 10 to about 50 g/l calculated as tin metal and is about 50to about 120 times the weight of the precious metal.

Usually the colloidal solution is about 1 or less in pH, i.e., stronglyacidic, and can be prepared in the conventional manner. For example, aprecious metal compound and a stannous compound are individuallydissolved in an acid solution and the resulting solutions are mixedtogether to give a colloidal solution. For use, the obtained colloidalsolution can be properly adjusted to a suitable concentration. Examplesof the acid solution useful in said procedure are a hydrochloric acidsolution, a sulfuric acid solution, a mixed solution of hydrochloricacid and sulfuric acid, a hydrochloric acid solution containing sodiumchloride, a sulfuric acid solution containing sodium chloride, a mixedsolution of hydrochloric acid and sulfuric acid containing sodiumchloride, etc.

Said colloidal solution may further contain copper lower aliphaticmonocarboxylate, copper bromide or the like. It is preferable to use adivalent copper compound as the copper compound because of its highsolubility. Of the copper lower aliphatic monocarboxylates, copperformate and copper acetate are preferred. When these compounds are used,a stable colloidal solution can be formed and can easily adhere in theform of a uniform film to the substrate to be treated. The amount of thecopper compound used is preferably about 0.2 to about 3 g /1, morepreferably about 0.5 to about 2 g/l, calculated as copper metal.

Especially preferred colloidal solutions useful as a catalyst solutioninclude, for example, an aqueous solution of hydrochloric acidcontaining about 150 to about 300 ppm, calculated as palladium metal, ofa palladium compound and about 10 to about 22 g/l, calculated as tinmetal, of an stannous compound.

The treatment with the colloidal solution is carried out by immersingthe substrate to be treated in a colloidal solution at about 10 to about50° C., preferably about 25 to about 45° C. for about 2 to about 10minutes, preferably about 3 to about 5 minutes. The treatment can form auniform catalytic film on the surface of the substrate.

Then, an electrically conductive coating is formed on the plastic moldedproduct with the catalyst applied, using an electroless copper platingsolution.

In the method of the invention, it is essential to use an electrolesscopper plating solution comprising a copper compound, a saccharidehaving a reducing property, a complexing agent and an alkali metalhydroxide. When said electroless copper plating solution is used, anelectrically conductive thin coating can be formed on the substrate tobe treated without developing a bridge deposit. The thin coating isproduced presumably due to the following deposition mechanism.

The saccharide contained as the reducing agent in said electrolesscopper plating solution has a significantly lower reducing power thanparaformaldehyde or the like conventionally used in known electrolesscopper plating solutions. Consequently a thin coating of copper isdeposited by reduction only on the palladium portion as a catalystmetal, but not on the tin portion having no catalytic property, wherebythe development of bridge deposit is prevented. The incompletelymetalized tin salt deposited on the substrate is partly reduced by theelectroless plating solution and partly dissolved. Then, the metalizedtin is replaced by copper and the copper is deposited on the substratewhile the dissolved-out tin is complexed by a complexing agent and ispresumably stabilized thereby.

Examples of the copper compound incorporated in the electroless copperplating solution are copper sulfate, copper chloride, copper carbonate,copper oxide, copper hydroxide and the like. The amount of the coppercompound used is about 0.1 to about 5 g/l, preferably about 0.8 to about1.2 g/l, calculated as copper metal. When the amount of the copper metalused is less than 0.1 g/l, an electroless plated copper coating isinsufficiently formed, and undesired deposition is induced byelectroplating in the subsequent step. Hence the lesser content isundesirable. On the other hand, if the amount of the copper metal usedexceeds 5 g/l, no effect is produced by the increase of copperconcentration and the required amount of the complexing agent isincreased in proportion to the copper concentration, resulting ineconomical disadvantage and in difficulty of effluent treatment.

Examples of the saccharide having a reducing property which isincorporated in the electroless copper plating solution are grape sugar,glucose, sorbitol, cellulose, cane sugar, mannitol, gluconolactone, etc.The amount of the saccharide used is about 3 to about 50 g/l, preferablyabout 10 to about 20 g/l. If less than 3 g/l of saccharide is used, acopper coating is insufficiently formed by electroless plating, andelectroplating entails a lower deposition capability in the subsequentstep. Hence it is undesirable. On the other hand, above 50 g/l, thestability of electroless copper plating solution is lowered and a platedcoating tends to show an inferior appearance. Hence it is undesirable.

Examples of the complexing agent to be incorporated into the electrolesscopper plating solution are hydantoin compounds, organic carboxylicacids, and the like. Useful hydantoin compounds are, for example,hydantoin, 1-methylhydantoin, 1,3-dimethylhydantoin,5,5-dimethylhydantoin, allantoin, etc. Examples of the organiccarboxylic acid are citric acid, tartaric acid, succinic acid and saltsof these acids. The complexing agents can be used either alone or incombination.

The amount of the complexing agent used is about 2 to about 50 g/l,preferably about 10 to about 40 g/l. If less than 2 g/l of thecomplexing agent is used, the complexing power is insufficient, and theability to dissolve copper is unsatisfactory, whereas the amountexceeding 50 g/l enhances the ability to dissolve copper but leads toeconomical disadvantage and difficulty of effluent treatment. Hence itis undesirable.

Further, since the saccharide with a low reducing power is used as areducing agent in said electroless plating solution, a hydantoincompound with a relatively low complexing power can be used as acomplexing agent without lowering the stability of the plating solution.When a plating solution contains a hydantoin compound with a relativelylow complexing power as a complexing agent, the solution has a highdeposition capability and effluent treatment is facilitated. The abovehydantoin compound has a slight complexing power for the tin salt drawninto the plating solution from the catalyst solution used in thepreceding step and thus can prevent adverse influence which arises fromthe tin salt. Consequently, it is suitable to use as the complexingagent a hydantoin compound alone or in combination with an organiccarboxylic acid. In the combined use, the amount of the organiccarboxylic acid is 50% by weight or less, preferably 20% by weight orless, based on the hydantoin compound used.

The foregoing electroless copper plating solution essentially containsan alkali metal hydroxide. Sodium hydroxide, potassium hydroxide,lithium hydroxide and the like are suitably used as the alkali metalhydroxide in view of availability and costs. These alkali metalhydroxides can be used either alone or in combination. The amount of thealkali metal hydroxide used is about 10 to about 80 g/l, preferablyabout 30 to about 50 g/l. Less than 10 g/l of alkali metal hydroxideresults in insufficient formation of electroless plated copper coatingand leads to a reduced deposition capability in electroplating over therange of low current density in the subsequent step. Hence it isundesirable. On the other hand, if the amount of the alkali metalhydroxide used is above 80 g/l, the solubility of copper is decreasedand the stability of the plating solution is lowered, with an increasein the concentration of the hydroxide. Hence it is undesirable.

In preparation of said electroless copper plating solution, it ispreferred to properly adjust the combination of components to be usedand the specific proportions of the components within theabove-mentioned proportion range of the components, such that the pH ofthe electroless plating solution is in the range of 10.0 to 14.0,preferably 11.5 to 13.5.

Optionally said electroless plating solution may further contain yellowprussiate, rhodanate and the like as a stabilizing agent. Since saidelectroless plating solution has a high stability, the solution canmaintain the high stability without use of a stabilizing agent or withuse of a small quantity, e.g. a few mg/l, of a stabilizing agent of lowstabilizing power such as tannic acid, rhodanine or the like.

In treatment with the electroless plating solution, the temperature ofelectroless copper plating solution is about 20 to about 70° C.,preferably about 35 to about 50° C. and the substrate to be treated isimmersed in this plating solution for about 30 seconds to about 20minutes, preferably about 3 to about 5 minutes. If the temperature ofthe plating solution is less than 20° C., a coating is insufficientlyformed by electroless plating. On the other hand, if the temperature ofthe plating solution is higher than 70° C., the solution is given a lowstability. Hence it is undesirable. If the substrate to be treated isimmersed in the plating solution for less than 30 seconds, a coating isinsufficiently formed by electroless plating. On the other hand, if theimmersion time is longer than 20 minutes, the resulting effect is nothigher than the effect achieved in the optimum range, and theproductivity is lower. Hence it is undesirable.

An electrically conductive very thin coating is formed on the surface ofthe substrate and electroplating can be conducted directly on thecoating. The obtained electrically conductive coating does not consistof copper alone. When the coating was dissolved in aqua regia and wasanalyzed by ICP, it was confirmed that the coating contained copper,palladium and tin.

Subsequently the substrate thus treated is electroplated in theconventional manner. Useful electroplating baths are not limited and canbe any of conventional electroplating baths. The electroplatingconditions can be conventional.

Electroplating methods for a decorating purpose comprising successivelyelectroplating a substrate with copper, nickel and chromium arespecifically described below as an example of electroplating methods.

A conventional bright copper sulfate plating solution can be used as acopper sulfate plating solution. For example, a plating bath to be usedin the invention is prepared by adding a conventional brightener to anaqueous solution containing about 100 to about 250 g/l of coppersulfate, about 20 to about 120 g/l of sulfuric acid, and about 20 toabout 70 ppm of chlorine ions. Copper sulfate plating conditions may beconventional. For example, electroplating is conducted at a platingsolution temperature of about 25° C. and a current density of about 3A/dm² and is continued until a deposit of the predetermined thickness isobtained.

A usual Watts bath can be used as a nickel plating solution. Usefulbaths are prepared by adding a commercially available brightener for anickel plating bath to an aqueous solution containing about 200 to about350 g/l of nickel sulfate, about 30 to about 80 g/l of nickel chlorideand about 20 to about 60 g/l of boric acid. Nickel plating conditionsmay be conventional. For example, electroplating is conducted at aplating solution temperature of about 55 to about 60° C. and a currentdensity of about 3 A/dm² and is continued until a coating of thepredetermined thickness is obtained.

A usual Sargent bath can be used as a chromium plating solution. Usefulbaths include an aqueous solution containing about 200 to about 300 g/lof chromic anhydride and about 2 to about 5 g/l of sulfuric acid.Chromium plating conditions are, for example, a plating solutiontemperature of about 45° C. and a current density of about 20 A/dm², andthe electroplating is continued until a deposit of the predeterminedthickness is obtained.

According to the present invention, the following remarkable effects canbe produced.

(1) Because the electroplating method of the invention does not cause abridge deposit which is likely to occur at the electroless plating stepin conventional methods of plating on plastics, a stardust-free coatingwith an esthetically pleasing appearance can be formed withoutcumbersome treatment such as brushing.

(2) The coating formed from the electroless plating solution for use inthe invention has a suitable electrical conductivity and theelectroplated coating of uniform thickness can be formed on said coatingin a short time. Because of this benefit, an electroplated coating witha superior appearance can be formed on a large-size substrate by simpleplating methods.

(3) The method of the invention eliminates the need to effect theactivation treatment (accelerator treatment) frequently done afterapplying the catalyst in the conventional plating method, and thus themethod is simplified.

(4) The method of the invention can prevent the occurrence of erosionblister which is likely to develop when an electroless nickel platingsolution is used as an electroless plating solution.

(6) Since the electroless copper plating solution for use in the methodof the invention contains a saccharide with relatively low reducingpower as a reducing agent, the plating solution is insusceptible todecomposition and has a high stability. Consequently a satisfactoryeffect can be achieved without use of the stabilizing agent contained inconventional electroless plating solutions or with use of a stabilizingagent having a low stabilizing power. Because of this feature, theplating is unlikely to stop due to the excess of a stabilizer, and theplating solution is insusceptible to decomposition attributable to thelack of a stabilizer. Accordingly, the plating solution is easy tocontrol.

(7) Even if the electroless copper plating solution contains a hydantoincompound with low complexing power as a complexing agent, the stabilityof the solution is not lowered. Thus when a hydantoin compound is usedas the complexing agent, the electroless plating solution is improved indeposition capability and effluent treatment is facilitated.

(8) The electroless copper plating solution is not only used in theplating method of the invention but also effectively used inpre-treatment for electroplating on ceramics.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention is described below in more detail with referenceto the following Examples.

EXAMPLE 1

A substrate to be treated was an automotive emblem made of an ABS resin(product of Mitsubishi Rayon Co. Ltd., trade name “3001 M”), measuring17 cm×3.8 cm ×0.3 cm (thickness) and having a surface area of about 1.3dm². A jig for use in plating operation had two contact points forcontact with the substrate to be treated, the two contact points beingspaced away by 11 cm. The jig was one constructed from a stainless steelrod and had a contact point portion with a diameter of 2 mm. The otherportion than the contact points was coated with a vinyl chloride sol,followed by baking.

First of all, the substrate to be treated was set in the jig, wasimmersed in a solution of an alkaline degreasing agent (product of OkunoChemical Industries Co., Ltd., trade name “ACE CLEAN A-220”, aqueoussolution containing 50 g/l of the product) at 50° C. for 5 minutes, waswashed with water and was immersed in an etching solution which was anaqueous solution containing 400 g/l of chromic anhydride and 400 g/l ofsulfuric acid at 67° C. for 10 minutes to give a rough surface to theresin substrate. Thereafter the substrate was washed with water,immersed in an aqueous solution containing 50 ml/l of 35% hydrochloricacid and 10 ml/l of a reducing agent (product of Okuno ChemicalIndustries Co., Ltd., trade name “TOP CATCH CR-200”) at room temperaturefor 30 seconds to remove the chromic acid from the surface of resinsubstrate and washed well with water.

Then, a pre-dip treatment was carried out by dipping the substrate intoan aqueous solution containing 250 ml/l of 35% hydrochloric acid at 25°C. for 1 minute. Thereafter the substrate was immersed in a colloidalsolution containing 330 mg/l of palladium chloride (200 mg/l of Pd), 35g/l of stannous chloride (18.5 g/l of Sn), and 350 ml/l of 35%hydrochloric acid with a pH of 1 or less at 45° C. for 4 minutes tocause a catalyst to uniformly adhere to the resin substrate.

Thereafter the substrate was washed with water and electroless platingoperation was conducted using the following electroless platingsolutions.

Bath 1 of the invention Copper sulfate 4 g/l Hydantoin 20 g/l Glucose 20g/l Sodium hydroxide 40 g/l pH 12.6 Temperature 40° C. Time 5 minutesBath 2 of the invention Copper sulfate 4 g/l 1-Methylhydantoin 20 g/lSorbitol 15 g/l Potassium hydroxide 45 g/l pH 12.8 Temperature 40° C.Time 5 minutes Bath 3 of the invention Copper sulfate 4 g/l1,3-Dimethylhydantoin 25 g/l Glucose 20 g/l Sodium hydroxide 25 g/lLithium hydroxide 20 g/l pH 12.8 Temperature 40° C. Time 5 minutes Bath4 of the invention Copper sulfate 3.5 g/l Allantoin 15 g/l Cane sugar 15g/l Sodium hydroxide 25 g/l Lithium hydroxide 40 g/l pH 13.8 Temperature40° C. Time 5 minutes Bath 5 of the invention Copper sulfate 5 g/lHydantoin 20 g/l Gluconolactone 10 g/l Potassium hydroxide 25 g/lLithium hydroxide 30 g/l pH 13.0 Temperature 40° C. Time 5 minutes Bath6 of the invention Copper sulfate 4 g/l 1-Methylol-5,5-dimethylhydantoin20 g/l Cane sugar 10 g/l Sodium hydroxide 25 g/l Lithium hydroxide 40g/l pH 13.0 Temperature 40° C. Time 5 minutes Bath 7 of the inventionCopper sulfate 5 g/l Citric acid 10 g/l Hydantoin 20 g/l Grape sugar 10g/l Potassium hydroxide 25 g/l Lithium hydroxide 40 g/l pH 13.0Temperature 40° C. Time 4 minutes Bath 8 of the invention Copper sulfate4 g/l Tartaric acid 20 g/l Mannitol 10 g/l Sodium hydroxide 25 g/lLithium hydroxide 35 g/l pH 12.8 Temperature 40° C. Time 5 minutesComparative Bath 1 Copper sulfate 10 g/l Sodium potassium tartarate 25g/l Formaldehyde 10 g/l 2,2-Dipyridyl 1 mg/l pH 12.4 Temperature 25° C.Time 10 minutes Comparative Bath 2 Copper sulfate 12 g/l EDTA · disodiumsalt 35 g/l Formaldehyde 10 g/l Sodium cyanide 5 mg/l pH 12.2Temperature 40° C. Time 7 minutes Comparative Bath 3 Nickel sulfate 25g/l Citric acid 20 g/l Ammonium chloride 20 g/l Sodium hypophosphite 18g/l Lead nitrate 1 mg/l pH 9.0 Temperature 40° C. Time 8 minutes

Then, the substrate was washed well with water and was subjected, asheld in the jig, to the subsequent copper electro-plating step. A copperplating solution was prepared by adding 5 ml/l of “CRP Copper MU” and0.5 ml/l of “CRP Copper A” (trade names, products of Okuno ChemicalIndustries Co., Ltd.) as a brightener to an aqueous solution containing250 g/l of copper sulfate, 50 g/l of sulfuric acid, and 50 ppm ofchlorine ions. A copper electroplating operation was performed at aplating solution temperature of 25° C. and a current density of 3 A/dm²for 20 minutes using a plate of phosphorus-containing copper as an anodeand the substrate to be plated as a cathode while effecting slow airagitation.

Then, the substrate was washed with water and electroplated with nickel.A nickel electroplating solution was prepared by adding 20 ml/l of “ACNAB-1” and 20 ml/l of “ACNA B-2,” (trade names, products of Okuno ChemicalIndustries Co., Ltd.) as a brightener to an aqueous solution containing250 g/l of nickel sulfate, 50 g/l of nickel chloride and 40 g/l of boricacid. A nickel electroplating operation was performed at a platingsolution temperature of 50° C. and a current density of 4 A/dm² for 15minutes using a plate of pure nickel as an anode and the substrate to beplated as a cathode while effecting slow air agitation.

Next, the substrate was washed with water and electroplated withchromium using, as a chromium plating solution, an aqueous solutioncontaining 250 g/l of chromic anhydride (trivalent chrome 3 g/l ) and2.0 g/l of sulfuric acid with a plate of lead as an anode and thesubstrate to be plated as a cathode at a plating solution temperature of50° C. and a current density of 25 A/dm² for 1 minute without agitation.

Some properties of the plated coatings formed by the above-mentionedmethod and some properties of the electroless plating solutions usedwere evaluated by the following methods with the results set forthbelow.

Deposition Capability of Electroplating

(Evaluation method) A period of time was determined until an automotiveemblem used as a substrate to be plated is covered with copper over itsentire surface of the emblem within a copper electroplating solution.

(Results) It took about 38 seconds to cover the entire surface of theautomotive emblem with each of Comparative Baths 1-3 used asconventional electroless plating solutions, whereas it took about 50seconds to cover the entire surface thereof with each of Baths of theInvention 1-8. However, this difference scarcely affected theproductivity.

Appearance of Coating After Electroplating

(Evaluation method) The occurrence or non-occurrence of pit and stardustand the degree of gloss after plating with chromium were evaluated byvisual inspection. (Results) When Baths of Inventions 1-8 were used,coatings of esthetically pleasing appearance were formed, and no flawwas found on the surface of each coating. On the other hand, whenComparative Bath 3 was used, the coating was imparted relatively goodappearance and only a few pits and a little stardust were found. WhenComparative Baths 1 and 2 were used, pits and stardust were developed.

Adhesion

(Evaluation method) A plate of ABS resin, 100 mm×100 mm, was coated byelectroless plating and a copper coating of 50 μm thickness was formedby copper sulfate electroplating on the plate. The coating was cut tothe surface of the ABS resin plate to give cuts with 10 mm width. Thecoating was peeled with an autograph and the peel strength wasdetermined.

(Results) When Baths 1-8 of the invention were used, the strength was inthe range of 1150 to 1280 g and average strength was 1220 g. The use ofComparative Bath 1 resulted in strength of 940 g; the use of ComparativeBath 2, strength of 980 g; and the use of Comparative Bath 3, strengthof 1010 g. All of comparative baths showed a lower adhesion than thebaths of the invention.

Solution Stability

(Evaluation method) Plating operation was carried out using each ofBaths 1-8 of the invention and Comparative Baths 1-3 at a totaldeposition area of 1.5 dm² per liter and the same procedure was repeated5 times. Thereafter Baths 1-8 of the invention were left to stand at 70°C.; Comparative Bath 1, at 35° C.; Comparative Bath 2, at 70° C.; andComparative Bath 3, at 60° C. A time period from the start of standingat such temperature until inducement of decomposition was determined.

(Results) No decomposition occurred even after a time lapse of 200 hourswith respect to Baths 1-8 of the invention. On the other hand,decomposition arose 22 hours later with respect to Comparative Bath 1, 8hours later with respect to Comparative Bath 2 and 66 hours later withrespect to Comparative Bath 3, which means that the comparative bathshad a low stability.

Solution Controllability

(Evaluation method) Coatings were produced by electroless plating undervarious conditions of the concentration of metals, pH, temperature andtime with respect to Baths 1-8 of the invention and Comparative Baths1-3. Then the coatings were electroplated with copper in the subsequentstep to determine the range of conditions in which a coating wasdeposited by electroplating.

(Results) A coating was formed by electroplating from the baths of theinvention under a wider range of each item of conditions than thecomparative bath. This confirmed that it was easier to control the bathsof the invention.

Effluent Treatment

(Evaluation method) Baths 1-8 of the invention and Comparative Baths 1-3were diluted to specific metal concentrations and were subjected to pHadjustment, coagulation, precipitation and filtration as done in a usualmethod of disposing waste water after which the amounts of remainingmetals were measured.

(Results) Baths 1-6 of the invention showed 3-5 ppm in the concentrationof remaining metals; Bath 7 of the invention, 22 ppm; and Bath 8 of theinvention, 42 ppm, whereas Comparative Bath 1 displayed 40 ppm in theconcentration of remaining metals; Comparative Bath 2, 65 ppm; andComparative Bath 3, 48 ppm. As apparent from the results, Baths 1-7 ofthe invention using a hydantoin compound as a complexing agent showedlower concentrations of remaining metals than the comparative baths.Especially significantly lower remaining metal concentrations wereexhibited by Baths 1-6 of the invention containing hydantoin alone.

As is clear from the results described above, Baths 1-8 of the inventionshowed higher performance characteristics in any of appearance,adhesion, solution stability, range in which the solution should becontrolled, and ease of effluent treatment than the comparative baths.The baths of the invention exhibited a slightly lower depositioncapability in electroplating than the comparative baths. However, sincecopper sulfate electroplating is generally effected for at least 30 to60 minutes, the difference in the deposition capabiltity scarcelyaffects the productivity. Thus the experiments confirmed excellentindustrial usefulness of the plating solution of the invention.

What is claimed is:
 1. A method of electroplating non-conductive plasticmoldings, the method comprising the steps of: applying a catalyst usefulfor electroless plating to non-conductive plastic moldings using acolloidal solution containing a precious metal compound and a stannouscompound; forming an electrically conductive coating on the surface ofthe moldings using an electroless copper plating solution consistingessentially of a copper compound, a reducing agent consisting of atleast one saccharide having a reducing property, a complexing agent andan alkali metal hydroxide; and electroplating the coated moldingswherein the electroless copper plating solution has a pH of 10 to 14 andthe reducing agent is contained in the electroless copper platingsolution in amounts sufficient to function as a reducing agent.
 2. Themethod according to claim 1, wherein the electroless copper platingsolution is an aqueous solution comprising 0.1 to 5 g/l, calculated ascopper metal, of the copper compound, 2 to 50 g/l of the complexingagent, 3 to 50 g/l of the saccharide having a reducing property, and 10to 80 g/l of the alkali metal hydroxide.
 3. The method according toclaim 1 or 2, wherein the saccharide having a reducing property is atleast one selected from the group consisting of grape sugar, glucose,sorbitol, cellulose, cane sugar, mannitol and gluconolactone, andwherein the complexing agent is at least one selected from the groupconsisting of hydantoin compounds and organic carboxylic acids.
 4. Themethod according to claim 1 or 2, wherein the complexing agent is ahydantoin compound alone or a mixture of a hydantoin compound and anorganic carboxylic acid, the amount of the organic carboxylic acid being50% by weight or less of the hydantoin compound.
 5. The method accordingto claim 1 or 2, wherein the electroless copper plating solution has apH of 10 to 14 and a solution temperature of 20 to 70° C.